U.S. patent application number 12/129926 was filed with the patent office on 2009-12-31 for methods and apparatus for assignment and maintenance of unique aircraft addresses for tis-b services.
Invention is credited to Graham C. Dooley.
Application Number | 20090322589 12/129926 |
Document ID | / |
Family ID | 41446731 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090322589 |
Kind Code |
A1 |
Dooley; Graham C. |
December 31, 2009 |
METHODS AND APPARATUS FOR ASSIGNMENT AND MAINTENANCE OF UNIQUE
AIRCRAFT ADDRESSES FOR TIS-B SERVICES
Abstract
Methods and apparatus for assigning a pseudo address to an
aircraft not equipped with an ADS-B transponder and maintaining the
assigned pseudo address over a number of regions each supported by
different TIS-B systems. In an exemplary embodiment, each TIS-B
system is assigned a range of addresses particular to the region in
which the TIS-B system is located.
Inventors: |
Dooley; Graham C.; (Snow
Hill, MD) |
Correspondence
Address: |
RAYTHEON COMPANY;C/O DALY, CROWLEY, MOFFORD & DURKEE, LLP
354A TURNPIKE STREET, SUITE 301A
CANTON
MA
02021
US
|
Family ID: |
41446731 |
Appl. No.: |
12/129926 |
Filed: |
May 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60941365 |
Jun 1, 2007 |
|
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Current U.S.
Class: |
342/37 |
Current CPC
Class: |
G08G 5/0008 20130101;
G01S 13/91 20130101; G01S 13/765 20130101; G08G 5/0078
20130101 |
Class at
Publication: |
342/37 |
International
Class: |
G01S 13/91 20060101
G01S013/91 |
Claims
1. A method, comprising: determining whether a track update for a
ADS-B unequipped aircraft correlates with an entry in a track file
for first TIS-B system for a first region, the first TIS-B system
having a first aircraft assignment processor with a first range of
addresses allocated to the first region, wherein the first TIS-B
system is adjacent to a second TIS-B system for a second region;
assigning, for a new entry in the track file for the aircraft, a
pseudo address for the aircraft from the first range of addresses;
publishing track updates for the aircraft from only a first one of
the first and second TIS-B systems, regardless of how many TIS-B
systems are actually tracking the aircraft; transmitting a message
to the second TIS-B system for the second region when the aircraft
enters a handoff region for the first region without requiring the
first TIS-B system to know which region will next provide coverage
for the aircraft; and maintaining the pseudo address assigned by
the first aircraft assignment processor for the aircraft in the
second regions along a route of flight.
2. The method according to claim 1, wherein the handoff region for
the first region and a handoff region for the second region are the
same region.
3. The method according to claim 1, wherein the first handoff
region has a distance ranging from about 5 miles to about 50
miles.
4. The method according to claim 1, wherein the new entry
corresponds to the aircraft taking off.
5. A system, comprising: a first TIS-B system for a first region
having a first handoff region, the first TIS-B system having a
first aircraft assignment processor to assign pseudo addresses to
an aircraft unequipped with an ADS-B transponder; a second TIS-B
system for a second region adjacent to the first region, the second
TIS-B system having a second aircraft assignment processor to
assign pseudo addresses to an aircraft unequipped with an ADS-B
transponder, wherein the first TIS-B system broadcasts a message
containing track information for the aircraft to the second TIS-B
system for the second region when an aircraft enters the first
handoff region without requiring the first TIS-B system to know
which region will next provide coverage for the aircraft, wherein
the pseudo address assigned to the aircraft by the first aircraft
assignment processor is used by the second TIS-B system for the
aircraft.
6. The system according to claim 5, wherein the aircraft assignment
processor has an assigned pool of addresses.
7. The system according to claim 5, wherein the first TIS-B system
broadcasts the message when the aircraft enters the first handoff
region.
8. The system according to claim 7, wherein the second TIS-B system
correlates track information for the aircraft in the broadcast
message with a target detected by radar.
9. The system according to claim 5, wherein the only a first one of
the first and second TIS-B system publishes track updates for the
aircraft.
10. An article, comprising: a computer-readable medium containing
stored instructions that enable a machine to perform the steps of:
determining whether a track update for a ADS-B unequipped aircraft
correlates with an entry in a track file for first TIS-B system for
a first region, the first TIS-B system having a first aircraft
assignment processor with a first range of addresses allocated to
the first region, wherein the first TIS-B system is adjacent to a
second TIS-B system for a second region; assigning, for a new entry
in the track file for the aircraft, a pseudo address for the
aircraft from the first range of addresses; publishing track
updates for the aircraft from only a first one of the first and
second TIS-B systems, regardless of how many TIS-B systems are
actually tracking the aircraft; transmitting a message to the
second TIS-B system for the second region when the aircraft enters
a handoff region for the first region without requiring the first
TIS-B system to know which region will next provide coverage for
the aircraft; and maintaining the pseudo address assigned by the
first aircraft assignment processor for the aircraft in the second
regions along a route of flight.
11. The article according to claim 10, further including
instructions for the first TIS-B system to broadcast the message
when the aircraft enters the first handoff region.
12. The article according to claim 11, further including
instructions for enabling the second TIS-B system to correlate
track information for the aircraft in the broadcast message with a
target detected by radar.
13. The article according to claim 10, wherein the handoff region
for the first region and a handoff region for the second region are
the same region.
14. The article according to claim 10, wherein the first handoff
region has a distance ranging from about 5 miles to about 50
miles.
15. The article according to claim 10, wherein the new entry
corresponds to the aircraft taking off.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application No. 60/941,365, filed on Jun. 1,
2007, which is incorporated herein by reference.
BACKGROUND
[0002] As described by the FAA (Federal Aeronautics
Administration), ADS-B is an air traffic control system that uses
signals from Global Positioning Satellites (GPS), instead of radar
data, to keep aircraft at safe distances from one another. The
ADS-B system provides air traffic controllers and pilots with
accurate information that will help keep aircraft safely separated
in the sky and on runways. With ADS-B some of the responsibility
for keeping safe distances between aircraft is shifted from air
traffic controllers on the ground to pilots who will have displays
in the cockpits showing air traffic around them.
SUMMARY
[0003] The present invention provides methods and apparatus for
assigning pseudo address to aircraft not equipped with ADS-B
transponders that must still be processed within a system that
monitors and reports the locations of all aircraft. The assigned
pseudo address assigned in one region is maintained across all
regions in the air space.
[0004] In one aspect of the invention, a method comprises
determining whether a track update for a ADS-B unequipped aircraft
correlates with an entry in a track file for first TIS-B system for
a first region, the first TIS-B system having a first aircraft
assignment processor with a first range of addresses allocated to
the first region, wherein the first TIS-B system is adjacent to a
second TIS-B system for a second region, assigning, for a new entry
in the track file for the aircraft, a pseudo address for the
aircraft from the first range of addresses, publishing track
updates for the aircraft from only a first one of the first and
second TIS-B systems, regardless of how many TIS-B systems are
actually tracking the aircraft, transmitting a message to the
second TIS-B system for the second region when the aircraft enters
a handoff region for the first region without requiring the first
TIS-B system to know which region will next provide coverage for
the aircraft, and maintaining the pseudo address assigned by the
first aircraft assignment processor for the aircraft in the second
regions along a route of flight.
[0005] In another aspect of the invention, a system comprises a
first TIS-B system for a first region having a first handoff
region, the first TIS-B system having a first aircraft assignment
processor to assign pseudo addresses to an aircraft unequipped with
an ADS-B transponder, and a second TIS-B system for a second region
adjacent to the first region, the second TIS-B system having a
second aircraft assignment processor to assign pseudo addresses to
an aircraft unequipped with an ADS-B transponder, wherein the first
TIS-B system broadcasts a message containing track information for
the aircraft to the second TIS-B system for the second region when
an aircraft enters the first handoff region without requiring the
first TIS-B system to know which region will next provide coverage
for the aircraft, wherein the pseudo address assigned to the
aircraft by the first aircraft assignment processor is used by the
second TIS-B system for the aircraft.
[0006] In a further aspect of the invention, an article comprises a
computer-readable medium containing stored instructions that enable
a machine to perform the steps of: determining whether a track
update for a ADS-B unequipped aircraft correlates with an entry in
a track file for first TIS-B system for a first region, the first
TIS-B system having a first aircraft assignment processor with a
first range of addresses allocated to the first region, wherein the
first TIS-B system is adjacent to a second TIS-B system for a
second region, assigning, for a new entry in the track file for the
aircraft, a pseudo address for the aircraft from the first range of
addresses, publishing track updates for the aircraft from only a
first one of the first and second TIS-B systems, regardless of how
many TIS-B systems are actually tracking the aircraft, transmitting
a message to the second TIS-B system for the second region when the
aircraft enters a handoff region for the first region without
requiring the first TIS-B system to know which region will next
provide coverage for the aircraft, and maintaining the pseudo
address assigned by the first aircraft assignment processor for the
aircraft in the second regions along a route of flight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing features of this invention, as well as the
invention itself, may be more fully understood from the following
description of the drawings in which:
[0008] FIG. 1 is a schematic diagram of an air traffic control
system having aircraft address assignment;
[0009] FIG. 1A is a schematic diagram of a multi-link air traffic
control system having aircraft address assignment;
[0010] FIG. 2 is a block diagram showing further detail for the air
traffic control system of FIG. 1;
[0011] FIG. 3 is a schematic diagram showing aircraft address
assignment in accordance with exemplary embodiments of the
invention;
[0012] FIG. 4 is a schematic diagram showing further details for
aircraft address assignment; and
[0013] FIG. 5 is a flow diagram showing an exemplary sequence of
steps for providing aircraft address assignment in accordance with
exemplary embodiments of the invention.
DETAILED DESCRIPTION
[0014] Before describing exemplary embodiments of the invention,
some introductory information is provided. In general, ADS-B
systems work by having aircraft receive GPS signals and use them to
determine the aircraft's precise location in the sky. The aircraft
avionics system uses this position for precise navigation, and also
broadcasts it along with other data from the aircraft's flight
monitoring system, such as the type of aircraft, its speed, its
flight number, and whether it is turning, climbing, or descending.
The data is automatically broadcast by the aircraft transponder
periodically (typically once or twice a second) using either the
1090 MHz Mode S Extended Squitter (1090ES) or the 978 MHz Universal
Access Transceiver (UAT). Both technologies are approved for use in
the National Airspace System (NAS), with 1090ES being predominantly
used by the commercial airlines and UAT being used by the General
Aviation community.
[0015] Aircraft equipped to receive the data, and ADS-B ground
stations up to 200 miles away, receive these broadcasts. ADS-B
ground stations add radar-based targets for non-ADS-B-equipped
aircraft to the mix and send the information back up to all
equipped aircraft on both frequencies--this function is called
Traffic Information Service-Broadcast (TIS-B). ADS-B ground
stations also send aircraft information from the national weather
service and flight information, such as temporary flight
restrictions--this is called Flight Information Service-Broadcast
(FIS-B).
[0016] Pilots see this information on their cockpit traffic display
screens. Air traffic controllers see the information on displays
they are already using, when adapted to process this data
source.
[0017] When properly equipped with ADS-B, both pilots and
controllers see the same real-time displays of air traffic. Pilots
will have much better situational awareness than in conventional
systems because they will know where their own aircraft is with
greater accuracy, and their displays will show them the aircraft in
the air around them. Pilots will be able to maintain safe
separation from other aircraft with fewer instructions from
ground-based controllers. At night and in poor visual conditions,
pilots will also be able to see where they are in relation to the
ground using on-board avionics and terrain maps.
[0018] ADS-B also increases airport and air corridor capacity,
because the more accurate tracking means aircraft will be able to
fly safely and more predictably with less distance between them.
And, because ADS-B accuracy also means better predictability, air
traffic controllers will be better able to manage the air traffic
arriving and departing from congested airports, resulting in even
more gains in capacity.
[0019] While radar technology has advanced, radar systems
occasionally have problems discriminating airplanes from migratory
birds and rain "clutter." Secondary surveillance radar (SSR)
systems can determine what objects are because they interrogate
transponders; however, both primary and secondary radars are very
large structures that are expensive to deploy, need lots of
maintenance, and require the agency to lease real estate to situate
them.
[0020] The automatic function of ADS-B eliminates the need for
action by a pilot and/or air traffic controller for the information
to be issued. The system has dependent surveillance aspect in that
the acquired surveillance-type information depends on the
navigation and broadcast capability of the source.
[0021] An ADS-B system includes a transmitter that includes message
generation and transmission functions at the source and a receiver
that includes message reception and report assembly functions at
the receiving vehicle or ground system.
[0022] An Air Traffic Control Radar Beacon System (ATCRBS) is used
in air traffic control (ATC) to enhance radar monitoring of
aircraft and aircraft separation. The system acquires information
for monitored aircraft and provides this information to the air
traffic controllers. This information can be used to identify
returns from aircraft and to distinguish those returns from ground
clutter.
[0023] The system includes aircraft transponders and secondary
surveillance radars (SSRs), installed at ATC locations. The SSR
transmits interrogations and listens for replies. The aircraft
transponders receive interrogations and determine whether to
reply.
[0024] An ATC ground station typically includes a primary
surveillance radar that transmits pulses and receives signal
returns from aircraft and a secondary surveillance radar (SSR)
having a main antenna and/or an omnidirectional antenna. A primary
receives signal returns from a target while the SSR receives
responses actively transmitted by an aircraft or other object. The
relatively high frequency pulses are known as interrogation.
[0025] The SSR system scans the area and transmits interrogations
over the scan area. The interrogations specify what type of
information a replying transponder should send by using a system of
modes, e.g., mode 1, mode 2, mode 3/A, mode 4 (IFF), Mode 5, and
mode C. Mode S is a discrete selective interrogation mode that also
facilitates TCAS for civil aircraft. In addition, it provides the
basis for the ADS-B communications link used by commercial aircraft
(i.e., enhanced mode S).
[0026] Commercial aircraft that fly mainly at high altitudes are
equipped with 1090ES capability, while General Aviation (GA)
aircraft flying at lower altitudes typically have UAT (Universal
Access Transceiver). This dual link approach does not provide
air-to-air ADS-B capability for aircraft equipped with only one
link technology. When both types of ADS-B link are in use, ADS-B
ground stations use ground-to-air broadcasts to relay ADS-B reports
received on one link to aircraft using the other link (ADS
rebroadcast, or ADS-R).
[0027] The TIS-B system completes the air surveillance picture by
providing surveillance target information derived from radar on the
ADS-B data links so that all ADS-B equipped aircraft can see all
aircraft in their vicinity, regardless of equipage. The ADS-B
ground station transmits the surveillance information derived from
radar on both ADS-B data links, as well as the ADS-R information on
the alternate link.
[0028] One issue for ADS-B is the capacity for carrying message
traffic from aircraft, as well as allowing a link, such as a radio
channel, to support legacy systems. The more message traffic there
is, the less aircraft can be supported due to bandwidth
limitations.
[0029] Another issue in ADS-B system is that the increasing volume
of air traffic and the emerging use of Automatic Dependent
Surveillance creates frequency congestion in the 1090 MHz spectrum
which reduces the efficacy of airborne and ground-based
surveillance. Reduction in frequency congestion has been a
motivation for development of Mode S radar, as well as the
development of monopulse SSR radar.
[0030] FIG. 1 shows an exemplary ADS-B system 10 having unique
aircraft address assignment module 17 for TIS-B services in
accordance with exemplary embodiments of the invention. The system
10 includes an ADS-B ground station 12 and a secondary surveillance
radar (SSR) 14 coupled via ADS-B ground infrastructure 16. A
weather service installation 18 communicates with an XM satellite
20 via an antenna 22. The weather service installation 18 and the
antenna uplink 22 are coupled to the ADS-B ground infrastructure
16.
[0031] The SSR 14 communicates via Mode C for some aircraft 24 and
via 1090ES for other aircraft 26. The ADS-B 12 communicates with
aircraft 26 while various aircraft 26, 28 can communicate directly
with each other. Some of the aircraft also receive messages from
the XM satellite 20.
[0032] In an exemplary embodiment, 1090ES is used for ADS-B and
TIS-B communication and XM satellite radio for FIS-B communication
with a distributed equipment network on the ground. This provides
increased capacity, accelerated equipage, and reduced deployment
cost compared with known systems.
[0033] A single link on 1090ES provides a number of advantages.
Antennas and transceivers for UAT link processing and redundant
1090ES transmitters for ADS-R availability is not required at the
ground station. In addition, ADS-R of UAT on 1090ES results in
equivalent congestion to all aircraft on 1090ES. Further, 1090ES
equipage based on Mode S transponders reduces ATCRBS interference.
By using a single link, there is no possibility of amplification
and rebroadcast of invalid signals, i.e., no spoofing. Also,
aircraft receive reports from other aircraft regardless of ground
system coverage or failure. UAT aircraft retain Mode C transponders
for operation with SSR and TCAS.
[0034] FIG. 1A shows a multi-link ADS-B air traffic control system
10' having unique aircraft address assignment module 17 for TIS-B
services in accordance with exemplary embodiments of the invention.
The system 10' supports aircraft with universal access transceivers
(UAT) 11 for communicating with a ground station. Air traffic
information is rebroadcast using an ADS-R function via 1090 link.
ADS-R interconnects the 1090ES link 13 and the UAT link 15. The
FIS-B 19 weather information is also provided via UAT
communication. TIS-B 21 provides aircraft traffic information to
aircraft. The operation and configuration of dual-link ADS-B
systems is well known to one of ordinary skill in the art.
[0035] While inventive embodiments of unique aircraft address
assignment for TIS-B services is shown and described in conjunction
with single and multi-link ADS-B type air traffic control systems,
it is understood that exemplary embodiments of inventive unique
aircraft address assignment for aircraft traffic services are
applicable to air traffic control systems in general in which it is
desirable to track aircraft over adjacent regions.
[0036] FIG. 2 shows further details of the system of FIG. 1, which
includes unique aircraft address assignment for TIS-B services 41
in accordance with exemplary embodiments of the invention. The
system is partitioned by capability with minimal dependencies
allowing independent integration, test, and deployment of ADS-B
surveillance, TIS-B and FIS-B services. Link specific processing is
separate to minimize the impact of link enhancements.
[0037] An aircraft 40 receives XM weather information from an FISB
service 42 and communicates via a 1090 MHz link processor 44 with
an ADS-B report and status (ADSS) service 46 and a TISB service 48.
The ADSS service 46, the TISB service 48, and the FISB service 42
are coupled to the SDP 50. The TISB service 48 receives weather
radar information and/or MLS from a service 52. The weather service
54 provides information to the FISB service 42.
[0038] A AWOS (automated weather observation service) user 56
receives observation and status information from an AWOS service
58. A surveillance network 60 exchanges packet data with an ALL
service 62, which exchanges command, response, alert, and status
information with a SMAC (system monitor and control) service
64.
[0039] In one aspect of the invention, in general, aircraft that
transpond an ADS-B signal have a pre-assigned address that is
inserted into the message to uniquely identify the aircraft.
Aircraft that are not equipped with ADS-B transponders must still
be processed within a system that monitors and reports the
locations of all aircraft. However, the TIS-B service does not have
any way to determine an equivalent identification directly from the
aircraft upon which it is reporting. In order to uniquely identify
these aircraft in the same way, a "pseudo" address is assigned. In
applications of the TIS-B service where assignment is performed in
multiple places to distribute processing load across a number of
regions, the system ensures that the pseudo assignment logic
assigns and maintains unique addresses across the entire airspace.
It does this by assigning addresses from mutually exclusive address
pools that are allocated on a regional basis.
[0040] Aircraft that originate in a particular region are assigned
an address from the range of addresses assigned to that region's
address allocation processor. The aircraft then retains that
assigned address across contiguous regions covered by the air
traffic control system. In an exemplary embodiment that uses
distributed tracking, multiple regional TIS-B trackers can
cooperate in order to ensure the uniqueness of addresses across the
entire National Airspace System (NAS).
[0041] Each processor is adapted with a geographic coverage area
that includes a buffer region around and within its perimeter. As
aircraft enter the buffer region, their corresponding track data,
including the assigned address, are shared among the processors to
ensure the preservation of the unique address as the aircraft
transits the airspace. Each processor checks that a track is about
to enter its airspace and discards the data if it is not. In this
way, it is not necessary to selectively notify adjacent
regions.
[0042] FIG. 3 shows an exemplary system in which a first TIS-B
system 100 includes an aircraft assignment processor 102 to assign
pseudo address for an aircraft 104 that does not have an ADS-B
transponder. The aircraft assignment processor 102 includes a range
of addresses 106 that are particular to that aircraft assignment
processor. If the aircraft 104 originates, e.g., takes off, in a
first region FR supported by the first TIS-B system 100, then the
aircraft assignment processor 102 for that system assigns the
pseudo address to the aircraft 104. Based on the assigned address,
the region of origination is known for the aircraft.
[0043] As the aircraft 104 enters into a first buffer region BR1
between the first region FR and a second region SR, which is
supported by a second TIS-B system 200, the pseudo address and
track data for the aircraft are transmitted from the first TIS-B
system 100 to all other systems (including, of course, the second
TIS-B system 200). The aircraft 104 is not assigned a new address
by the second TIS-B system 200, but rather retains the original
unique pseudo address assigned by the first TIS-B system 100.
[0044] In an exemplary embodiment, track data in the buffer areas
are shared among the TIS-B systems 100, 200, 300 so that each
system can associate aircraft that are being tracked in its
respective coverage area with tracks that are exiting adjacent
areas, and therefore already have an address assignment. With this
arrangement, a non-ADS-B equipped aircraft can be assigned a unique
pseudo address that is maintained across multiple coverage regions.
In addition, the region from which the aircraft originated can be
easily identified.
[0045] One of ordinary skill in the art will readily appreciate
that the various functionality described in the exemplary
embodiments contained herein can be implemented in a variety of
configurations, architectures, and hardware and software
partitions. For example, computer readable instructions can be
provided a on a disk 99, for example, to enable a machine to
perform processing steps.
[0046] FIG. 4 shows an exemplary configuration of first, second,
and third regions A, B, C. The first region A includes a handoff
region HA generally defined by a selected distance from the outer
perimeter of the region. Similarly, the second region B includes a
handoff region HB and the third region C includes a handoff region
HC. Each region has a respective TIS-B system TISA, TISB, TISC.
Each TIS-B system maintains a track file TF containing track
information for each target, e.g., aircraft, within the region.
Each system includes an aircraft assignment processor module AAP to
assign psuedo addresses from the pool of region addresses to
non-ADS-B equipped aircraft, as described above in conjunction with
FIG. 3.
[0047] It is understood that the size, distance, etc of the handoff
region can vary to meet the needs of a particular application. In
an exemplary embodiment, the handoff region ranges from about 5 to
about 50 miles as measured by the shortest distance for an aircraft
to traverse the handoff region. In one embodiment, the handoff
region is about 10 miles in distance.
[0048] An aircraft takes off from a location L in the first region
A. The aircraft assignment processor AAPA of the first TIS-B system
TISA for the first region A assigns a unique address for the
aircraft from the address pool for the first region and updates the
track file TF for the aircraft. As shown, the aircraft travels
toward the second region B. The aircraft travels through the first
region A, the first handoff area HA, the second handoff region HB,
and into the second region B. When the aircraft enters the first
handoff region HA the first TIS-B system TISA broadcasts a message
containing the track info for the aircraft to the other TIS-B
systems in the entire coverage area (e.g., the NAS), including
TISB, TISC. The second TIS-B system TISB in the second region B
determines that the aircraft will be entering the second region B
and begins creating and updating an entry in its track file. When
the aircraft is detected by sensors (e.g., radar) within region B,
the newly detected track associated with the aircraft is correlated
with the track just notified from region A. Consequently, the
second aircraft assignment processor AAPB does not generate a new
address for the aircraft as the address generated by the first
TIS-B system TISA is used.
[0049] FIG. 5 shows an exemplary sequence of steps for assignment
of unique addresses for aircraft. In step 500, upon detection of an
aircraft in its sensor (e.g., radar) coverage area, the TIS-B
system checks if the track is within the adapted geographic
boundary defining its own region. Tracks outside its region can be
discarded. The TIS-B system then checks in step 502 if the newly
detected track correlates with an entry in its track file, such as
by checking the source track ID, position, etc. For existing track
file entries, the track file is updated and the existing aircraft
address is added to track update messages in step 504. For new
entries, in step 506, a new aircraft address is allocated from the
region's address pool. For example, when the aircraft in FIG. 4
takes off a new aircraft address for the first region is allocated.
In step 508, the track update is published as part of the TIS-B
service. Track updates are published as long as the track remains
in that region. This also ensures that only one TIS-B regional
system will be publishing updates for a specific aircraft, thereby
avoiding redundant updates that take up data link bandwidth.
[0050] In step 510, when an aircraft approaches a region boundary,
such as in FIG. 4 the aircraft heads out of the first region A into
the second region B, the track update is transmitted to all TD (TIS
distribution) components, such as via a separate multicast address
message. The regional TD components subscribe to the handoff
multicast group. For each track received on this address, in step
512 each TD checks if the track position lies within the handoff
region. The message is ignored if the track is not about to enter a
region. For example, when the second TIS-B system TISB in the
second region B `sees` that the aircraft is within 10 miles of the
second region boundary, the system checks if the track has the
aircraft address in its track file. If so, in step 514, the system
updates the entry in the track file with the new track state and
notes the source track id (source track id's are associated with a
specific sensor). In not, in step 516, the system creates a new
entry, including the source track id. Note that a TD track entry
may have many source track ids associated with it, dependent on the
number of sensors (e.g., radars) covering that aircraft. Creation
of a new track file entry can occur as the aircraft first crosses
into the handoff region before it is detected within the new
region--whether this situation occurs is dependent on radar
coverage conditions.
[0051] As the track proceeds to enter the second region, Region B
in FIG. 4, the TD for the first region TIS-B system TISA ceases
publishing the track and the TD for region B will begin publishing
the track report. The second region TIS-B system TISB does not
assign a new address for the aircraft but rather uses the pseudo
address assigned in the first region A.
[0052] Exemplary embodiments of the invention are shown having
illustrative partitions of hardware and software. Alternative
embodiments having different apportionment between hardware and
software to meet the needs of a particular application will be
readily apparent to one of ordinary skill in the art. In addition,
the inventive processing can be implemented in computer programs
executed on programmable computers/machines that each includes a
processor, a storage medium or other article of manufacture that is
readable by the processor (including volatile and non-volatile
memory and/or storage elements), at least one input device, and one
or more output devices.
[0053] The system may be implemented, at least in part, via a
computer program product, (e.g., in a machine-readable storage
device), for execution by, or to control the operation of, data
processing apparatus (e.g., a programmable processor, a computer,
or multiple computers)). Each such program may be implemented in a
high level procedural or object-oriented programming language to
communicate with a computer system. However, the programs may be
implemented in assembly or machine language. The language may be a
compiled or an interpreted language and it may be deployed in any
form, including as a stand-alone program or as a module, component,
subroutine, or other unit suitable for use in a computing
environment.
[0054] A computer program may be deployed to be executed on one
computer or on multiple computers at one site or distributed across
multiple sites and interconnected by a communication network. A
computer program may be stored on a storage medium or device (e.g.,
CD-ROM, hard disk, or magnetic diskette) that is readable by a
general or special purpose programmable computer for configuring
and operating the computer when the storage medium or device is
read by the computer.
[0055] Having described exemplary embodiments of the invention, it
will now become apparent to one of ordinary skill in the art that
other embodiments incorporating their concepts may also be used.
The embodiments contained herein should not be limited to disclosed
embodiments but rather should be limited only by the spirit and
scope of the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
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